If a woman doesn't know that her husband is gambling, then it's already a marriage full of lies. It means she doesn't know her husband and doesn't know what he's doing.
A married friend of mine had to sell his luxury car because of gambling. When he sold the car, his wife found out he was gambling, and now they constantly fight.
A husband that hides his gambling activities from his wife might as well be cheating and he's hiding it since he's good at hiding something. There's no way a gambler is suppose to be with you and you'll not noticed some signs that they're gambling therefore if they can successfully do that then you should know that there are other things that they're hiding. As a husband, your wife should know things like you being a gambler because it'll be better that way than her finding out later and it becomes a problem. But the wife too should be considerate because maybe the husband was ashamed of telling the wife that he has gambling issues.